This invention relates to a tail unit for an aircraft.
The tail unit of an aircraft, which conventionally comprises a vertical fin and a pair of generally horizontal tailplanes, is a critical component with regard to the aircraft's performance and handling characteristics. Accordingly, the design of the tail unit is of considerable importance.
Unfortunately, the requirements for the tail unit vary substantially between low and high speed situations. At low speeds the horizontal tailplanes are important for the stability and control of an aircraft; at high speeds, however, they are substantially unnecessary and only serve to increase drag. This means that for high-speed, especially supersonic, aircraft a choice has to be made between designing the tail unit for high-speed flight, in which case the aircraft may be unstable during take-off and landing, or for low-speed performance. In practice the design tends to be an uneasy compromise between these extremes.
Accordingly it would be desirable to be able to vary the tail configuration in response to aircraft speed, but at the same time the tail plane must be operable to provide conventional aerodynamic control.